Annular ring shaped getter devices are well known in the art and have been described, for example, in U.S. Pat. Nos. 3,151,736; 3,381,805 and 3,385,420. In order to have a higher yield of getter metal from such devices it has also been common practice to enlarge or widen the annular channel. Such "wide channel" getter devices have been described in U.S. Pat. Nos. 3,719,433 and 4,642,516.
However, even wide channel getters do not allow the evaporation of getter metal vapours in sufficient quantity without incurring the risk of detachment of getter metal vapour releasing material from its holder or even melting of the getter container walls.